Citations

BACKGROUND Cystic adventitial disease (CAD) and intraneural ganglion cysts (IGCs) are rare mucinous lesions typically linked to an articular origin via macroscopic conduits. While secondary propagation between vascular and neural systems may occur through shared fascial sheaths, a direct microvascular route has not been previously described. OBSERVATIONS A 60-year-old man presented with progressive left tibial neuropathy. High-resolution 7T MRI and surgery revealed a large popliteal CAD lesion connecting to the knee joint via the middle genicular artery, alongside a secondary tibial IGC lacking an independent articular nerve connection. Findings demonstrated that high-pressure CAD mucin tracked along a small connecting vascular branch, creating a novel microvascular arterio-neural pathway to infiltrate the tibial nerve. Targeted articular branch disconnection and cyst decompression yielded significant clinical improvement, with no recurrence on 7-month follow-up 7T MRI. LESSONS This case expands the unifying articular theory, demonstrating that synovial fluid propagation can exploit a microvascular arterio-neural pathway rather than strictly macroscopic fascial planes. High-resolution 7T MRI is essential for visualizing these subtle connections. Successful management requires meticulous identification and disconnection of the primary joint connection to prevent recurrence. https://thejns.org/doi/10.3171/CASE26411

OBJECTIVE Schwannomas in the tibial, plantar, or medial calcaneal nerves around the ankle can mimic symptoms of tarsal tunnel syndrome. Outcomes after resection of schwannomas from these nerves have mainly been reported in case reports. The objectives of this study were to investigate the presentation and results for resection of schwannomas around the tarsal tunnel in a large case series and systematically review the currently available literature. METHODS Data from 40 patients (27 sporadic and 13 schwannomatosis cases) treated at 2 centers were retrospectively analyzed for preoperative type and duration of symptoms, schwannoma size at presentation, and outcome after resection. The following different locations around the ankle were compared: proximal to the tarsal tunnel (PTT), at the tarsal tunnel (ATT), and distal to the tarsal tunnel (DTT). The severity of symptoms was categorized in increasing order for pain only on touch, during load-bearing activities, and symptoms also at rest. Surgical outcome was assessed based on pain relief and occurrence of complications. The systematic literature review was performed using a PubMed and Embase search. RESULTS All but 1 patient presented with pain, local at the ankle, or neuropathic pain during weight-bearing activities (13/40, 32.5%). More than half of the patients also experienced symptoms at rest (52.5%). In 14 cases, the schwannoma was located PTT, in 17 cases ATT, and in 9 cases DTT in the plantar nerves. There were no significant differences in size and symptom duration at presentation for the different locations. Tumor size did not correlate with symptom severity. Outcomes after resection were excellent, with complete pain relief in all but 1 patient (97.0%). Complications included wound infection (5%) and temporary decreased sensation on the heel (7.5%). A review of 44 previously reported cases also frequently showed complete pain relief after resection. CONCLUSIONS The results of this study show that schwannomas around the tarsal tunnel often present with severe pain symptoms, even if the lesion is still relatively small. Resection frequently results in excellent pain relief. During surgery, it may not be necessary to open the entire length of the tarsal tunnel, thereby limiting the size of the incision, especially in schwannomas located proximally or distally to the tarsal tunnel.

BACKGROUND AND OBJECTIVES: Intraneural ganglion cysts (IGCs) can arise in different nerves but are uncommon in the tibial nerve (TN) and its branches near the ankle. According to the unified articular theory, a joint connection is always present in IGCs. This study aimed to identify joint connections of tibial-region IGCs and characterize their clinical, radiological, and propagation patterns. METHODS: A prospectively collected international database of >1100 IGCs was reviewed to identify tibial and medial plantar nerve (MPN) and lateral plantar nerve (LPN) IGCs around the ankle. RESULTS: Sixty-two ankle region IGCs were identified: 29 involving the TN (46.8%), 25 the MPN (40.3%), and 4 the LPN (6.4%); in 4 cases, the parent nerve was indeterminate. Thirty-one (50%) cases demonstrated joint connections. Of these, all TN at/distal to the tarsal tunnel (n = 4/4, 100%), MPN (n = 16/16, 100%) and LPN IGCs (n = 2/2, 100%) had a connection to the subtalar (ST) joint. A tibial IGC just proximal to the tarsal tunnel was connected to the tibiotalar (TT) joint in 75% of cases (n = 3/4) and the ST joint in 25% of cases (n = 1/4). Surgical ligation/disconnection of the articular branch was associated with markedly lower recurrence (0/13, 0%) compared with incision or resection of cyst without ligation (8/29, 27.6%; P = .04). CONCLUSION: Our findings support the unified articular theory. All IGCs in the ankle primarily ascend. Two distinct propagation patterns emerged: (1) those that ascend and enter the parent nerve proximal to the tarsal tunnel continue to ascend in the leg, without affecting the plantar nerves, and (2) those that ascend and enter the parent nerve at/distal to the tarsal tunnel have the potential to undergo crossover at the TN bifurcation and subsequently descend down the plantar nerves seen only in ST-origin cysts. Recognizing these pathways enhances diagnostic accuracy, directs identification of the joint of origin, and guides articular branch disconnection to reduce recurrence.

BACKGROUND Intraneural ganglion cysts (IGCs) are mucinous lesions that originate from adjacent synovial joints. According to the articular theory, synovial fluid tracks from a joint into the parent nerve through an articular branch. In uncommon sites such as the sural nerve, this connection can be difficult to identify. This report illustrates the use of a preoperative intra-articular fluorescein injection as a tool to identify the articular branch during surgery. OBSERVATIONS A 60-year-old woman presented with lateral foot pain, numbness, and a palpable mass along the left sural distribution. MRI showed a large cyst extending along the course of the sural nerve with connection to the subtalar joint. Fluorescein was injected preoperatively into this joint to detect the articular branch intraoperatively with ultraviolet illumination. The connection was transected at the joint origin, and the cyst was decompressed, preserving the parent nerve. Postoperatively, the patient had complete pain relief and sensory recovery, and MRI at 3 and 8 months confirmed resolution of the cyst. LESSONS Sural IGCs conform to the articular theory and can be managed effectively by transection of the articular branch. Preoperative intra-articular fluorescein injection is a useful tool to detect the articular branch that can be difficult to find in sural IGCs. https://thejns.org/doi/10.3171/CASE251018

ABSTRACT The paraneurium is a distinct connective tissue sheath that loosely envelopes the epineurium. The space between the para‐ and epineurium (the subparaneurial compartment) holds significant clinical relevance, serving as a target for deposition of regional anesthesia and a potential pathway for the pathological spread of cysts and tumors. However, visualization of the paraneurial layer, as a separate structure from the epineurium, remains challenging with conventional MRI, especially in the absence of pathology. This study evaluated the visualization of the paraneurium using ultra‐high‐field 7‐Tesla (7 T) MRI compared to conventional field strengths. We assessed normal nerve anatomy and a spectrum of pathological cases, including intraneural ganglion cysts, schwannomas, intraneural perineuriomas, and metastatic melanoma. The results demonstrated that 7 T MRI provides superior resolution and delineation of the paraneurium compared to 1.5 and 3 T systems. In normal anatomy, T1‐weighted and proton density (PD) sequences provided optimal contrast between the paraneurium and surrounding adipose tissue. In contrast, for pathological cases, T2‐weighted sequences with fat suppression were superior for depicting the paraneurium and identifying subparaneurial involvement. In conclusion, 7 T MRI offers a significant advantage in identifying the thin paraneurial layer. This capability provides valuable insights into the pathogenesis of tumor spread and holds promise for improving pre‐operative planning and clinical decision‐making in peripheral nerve pathology.

BACKGROUND Recently, the distribution of subparaneurial ganglion cysts involving the common peroneal and tibial nerves was described based on MRI analysis. Crossover in extreme cases was observed at the sciatic bifurcation through a mechanism comparable to a geyser, enabled by fenestrations in the epi- and paraneurium at the level of the bifurcation. The goal of this study was to investigate whether the geyser theory for crossover holds for other locations. OBSERVATIONS The authors’ prospectively maintained database of > 1100 cases of intraneural ganglion cysts in the world’s literature was queried for the existence of subparaneurial ganglion cysts at locations other than the knee. A previously unrecognized case involving the ulnar nerve originating from the elbow joint was found. Reinterpretation of the patient’s MRI studies showed circumferential subparaneurial distribution of a cyst over a long distance. Based on their previously reported geyser theory, the authors wondered if crossover had occurred at the level of the medial cord. A fenestration in the epi- and paraneurium at this level was confirmed on histological analysis of a normal cadaveric specimen. LESSONS This illustrative case shows that the geyser theory also holds in other locations. Surgical treatment of these subparaneurial cysts still follows the principles of the unified articular theory. https://thejns.org/doi/10.3171/CASE25671

OBJECTIVE Resection of common peroneal nerve (CPN) schwannomas is generally believed to be associated with a high risk of postoperative deficit, especially the chance for development of a foot drop. The goal of this study was to investigate the surgical results for resection of schwannomas from the CPN around the knee and specifically the chance of developing a postoperative motor deficit. METHODS Data from 36 patients with sporadic schwannomas and 8 patients with schwannomatosis (12 schwannomas total) treated at two centers were retrospectively analyzed. For sporadic cases, different locations around the knee were compared (i.e., proximal to the fibular head [FH], at the FH, and distal to the FH), taking into account the preoperative duration of symptoms, size at presentation, and surgical results of resection. The literature was systematically reviewed for reported cases by searching the PubMed and Embase databases. RESULTS A total of 24 schwannomas proximal to the FH were surgically treated: 11 at the FH, and 13 distal to the FH. For the entire cohort, the mean size of CPN schwannomas distal to the FH at presentation was smaller (1.4 × 1.8 cm) compared with those proximal to (2.0 × 2.2 cm) and at (2.2 × 2.3 cm) the FH, although these differences were not statistically significant. The mean preoperative duration of symptoms was slightly longer for schwannomas distal to the FH (35 months) than for those proximal to the FH (21 months) and at the FH (27 months); however, this difference was not significant. Postoperative deficits occurred in 3 sporadic cases: 2 patients with temporary weakness (Medical Research Council grade 4) that completely resolved within several months and 1 patient who had previously undergone surgery elsewhere and presented with deficits and in whom weakness increased after resection. Improvement in preoperative deficits was observed in 1 patient with extensor hallucis longus muscle paralysis that completely recovered. One patient with schwannomatosis developed muscle weakness after resection of a plexiform schwannoma. A systematic review of 21 previously reported cases in the literature showed that larger CPN schwannomas (> 5 cm) were more likely to result in permanent motor deficits. CONCLUSIONS This retrospective study of 44 patients shows that peroneal nerve schwannomas around the knee can be safely removed with a low risk of deficits. The systematic review of the literature suggests that larger schwannomas are more likely to result in permanent deficit. In the authors’ opinion, CPN schwannomas can best be resected, preferably when the lesion is relatively small.

ABSTRACT The microvasculature of peripheral nerve not only is important for the understanding of the development of compression syndromes, but it plays a critical role in the evolution of other nerve pathologies, including, for example, the distribution of intraneural ganglion cysts and lymphoma. We investigated the anatomical course of vessels around the human sciatic nerve and its bifurcation in eight human cadavers. Specifically, the presence of fenestrations on the epineurium and paraneurium's thickness in relation to the intraneural vessels was investigated. The sciatic, tibial, peroneal and sural nerves at the level of the bifurcation are surrounded by different layers, including the epineurium and paraneurial layers. Multiple fenestrations were observed in all membranes surrounding these nerves, which formed openings for the transfer of adipocytes and vessels from one compartment to the neighboring one. The openings were relatively large compared to the size of the vessels. In conclusion, vessels always travel through a natural opening in the paraneurial and epineurium. These vessels are important connections between the extrinsic and intrinsic nerve vasculature. In addition, the fenestration provides an important anatomical explanation for the possibility of transfer of anesthetic agents or different nerve pathologies, including intraneural ganglion cyst and tumors.

OBJECTIVE The formation and propagation of intraneural ganglion cysts (INGCs) is being elucidated by the unified articular theory. Its principles include a connection for joint fluid to egress from a synovial joint via an articular branch to a parent nerve and cyst following the path of least resistance, dependent on pressures and pressure fluxes. The occurrence of so-called extreme peroneal or tibial INGCs in the popliteal fossa extending to the sciatic nerve has been reported. One rarely described variant with a circumferential cyst within the subparaneurial compartment outside the epineurium of nerve(s) has been previously illustrated, but its mechanism and morphology have not been clarified. In this study, the authors aimed to investigate this type of cyst to challenge the principles of the unified articular theory. METHODS Four novel cases of patients with peroneal INGCs and "extreme subparaneurial cyst(s)" of the sciatic nerve and its distal branches were investigated: 3 arose from the superior tibiofibular joint (STFJ) and 1 from the knee joint. Three other cases of recognized extreme subparaneurial cyst (2 peroneal and 1 tibial from the STFJ) and 1 case of a peroneal subparaneurial cyst in the literature were reinterpreted. Data on clinical presentation, MR images, and surgical results were analyzed. RESULTS In all 8 cases, subparaneurial extension was observed to different degrees along the sciatic, tibial, common peroneal, sural, and deep and superficial peroneal nerves, as was subparaneurial-to-subparaneurial communication at the sciatic nerve bifurcation (i.e., crossover). Sequential MRI performed in 7 patients showed variable dynamic changes, including extreme ascent and descent. Extraneural rupture of the subparaneurial cyst, with spread into the surrounding tissue, was present at the sciatic nerve bifurcation in 6 cases. CONCLUSIONS The authors provide pathoanatomical and pathophysiological evidence supporting that extreme subparaneurial cysts follow the principles of the articular theory. They propose a distribution pattern that explains the occurrence and evolution of extreme subparaneurial cysts along the sciatic nerve and its distal branches in patients with peroneal or tibial INGCs and subepineurial cysts. Crossover in the subparaneurial compartment allows potentially extensive circumferential distribution within connected nerves. Also, dynamic factors can lead to dramatic changes in cyst size and appearance from reabsorption or extraneural rupture. In Part 2 of this study, the authors provide evidence showing that a fenestration in the epineurium allows cysts to pass from the subepineurial-to-subparaneurial, subparaneurial-to-subparaneurial, and subparaneurial-to-subepimyseal compartments.